(Fdefvar): Warn when var is let-bound but globally void.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index adff3e8670c..e8a8e4668e4 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -786,6 +786,21 @@ usage: (defvar SYMBOL &optional INITVALUE DOCSTRING)  */)
     {
       if (NILP (tem))
         Fset_default (sym, Feval (Fcar (tail)));
+      else
+        { /* Check if there is really a global binding rather than just a let
+             binding that shadows the global unboundness of the var.  */
+          struct specbinding *pdl = specpdl_ptr;
+          while (--pdl >= specpdl)
+            {
+              if (EQ (pdl->symbol, sym) && !pdl->func
+                  && EQ (pdl->old_value, Qunbound))
+                {
+                  message_with_string ("Warning: defvar ignored because %s is let-bound",
+                                       SYMBOL_NAME (sym), 1);
+                  break;
+                }
+            }
+        }
       tail = Fcdr (tail);
       tem = Fcar (tail);
       if (!NILP (tem))